The present invention relates to derivatives of 3,4-diaminofurazan useful as insensitive high explosive materials.
The synthesis of 3,4-diaminofurazan was first reported by Coburn in J. Heterocyclic Chem., vol. 5, pp. 83-87 (1968). Since then a large body of work has been accumulated on the oxidation of 3,4-diaminofurazan, especially by Russian scientists, e.g., Solodyuk et al., in Zh. Org. Khim., vol. 17(4), pp. 756-759 (1981) wherein the compounds 3,3xe2x80x2-diamino-4,4xe2x80x2-azoxyfurazan (DAAF) and 3,3xe2x80x2-diamino-4,4xe2x80x2-azofurazan (DAAzF) were described. They used a variety of peroxide reagents on 3,4-diaminofurazan to prepare 3,3xe2x80x2-diamino-4,4xe2x80x2-azoxyfurazan (DAAF), 3,3xe2x80x2-diamino-4,4xe2x80x2-azofurazan (DAAzF) and 3-amino-4-nitrofurazan usually as mixtures which were separated by differing solubilities. However, no characterization of the explosive properties of these compounds was reported.
One previously known explosive formulation included a combination of 2,2xe2x80x2,4,4xe2x80x2,6,6xe2x80x2-hexanitrostilbene (HNS) and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). While this formulation has been useful, it suffers some drawbacks in terms of performance and safety. Improved formulations including TATB have been sought.
The present inventors undertook a study of the compounds 3,3xe2x80x2-diamino-4,4xe2x80x2-azoxyfurazan (DAAF) and 3,3xe2x80x2-diamino-4,4xe2x80x2-azofurazan (DAAzF). Through their efforts, it was found that the compounds 3,3xe2x80x2-diamino-4,4xe2x80x2-azoxyfurazan (DAAF) and 3,3xe2x80x2-diamino-4,4xe2x80x2-azofurazan (DAAzF) were both useful as insensitive high explosive materials. In addition, an improved synthesis of 3,3xe2x80x2-diamino-4,4xe2x80x2-azofurazan (DAAzF) was developed. Also, formulations of 3,3xe2x80x2-diamino-4,4xe2x80x2-azofurazan (DAAzF) and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) should overcome the drawbacks of TATB/HNS formulations.
It is an object of this invention to provide an improved process for preparation of 3,3xe2x80x2-diamino-4,4xe2x80x2-azofurazan (DAAzF).
Another object of the present invention is to provide for use of 3,3xe2x80x2-diamino-4,4xe2x80x2-azoxyfurazan (DAAF) and 3,3xe2x80x2-diamino-4,4xe2x80x2-azofurazan (DAAzF) as insensitive high explosive materials.
Still another object of the present invention is to provide formulations including 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) and 3,3xe2x80x2-diamino-4,4xe2x80x2-azofurazan (DAAzF).
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention provides for the use of 3,3xe2x80x2-diamino-4,4xe2x80x2-azoxyfurazan (DAAF) and 3,3xe2x80x2-diamino-4,4xe2x80x2-azofurazan (DAAzF) as insensitive, high explosive materials.
The present invention further provides a process for the preparation of 3,3xe2x80x2-diamino-4,4xe2x80x2-azofurazan (DAAzF) from 3,4-diaminofurazan.
The present invention further provides a composition including 3,3xe2x80x2-diamino-4,4xe2x80x2-azofurazan and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB).
The present invention is concerned with insensitive, high explosive materials. The particular insensitive, high explosive materials of the present invention include 3,3xe2x80x2-diamino-4,4xe2x80x2-azoxyfurazan (DAAF) and 3,3xe2x80x2-diamino-4,4xe2x80x2-azofurazan (DAAzF). Neither compound has previously been known as insensitive, high explosive material.
In addition to the use of these particular compounds as insensitive, high explosive materials, the present invention is concerned with compositions including 3,3xe2x80x2-diamino-4,4xe2x80x2-azofurazan and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB).
By the term xe2x80x9cinsensitivexe2x80x9d, it is generally meant that the material has a drop height of greater than 320 cm as measured by using a 2.5 kg falling weight (Type 12).
Both 3,3xe2x80x2-diamino-4,4xe2x80x2-azoxyfurazan (DAAF) and 3,3xe2x80x2-diamino-4,4xe2x80x2-azofurazan (DAAzF) derive a significant amount of their energy of detonation from their intrinsically high heats of formation (xcex94Hf) and not from oxidation of carbon in the backbone. This, in a large part, is due to the presence of the azo- and azoxy-linkage. As an example of this, 3,3xe2x80x2-diamino-4,4xe2x80x2-azofurazan only has enough available oxygen to burn its hydrogen to water and none to oxidize carbon, yet it has better explosive performance than HNS (2,2xe2x80x2,4,4xe2x80x26,6xe2x80x2-hexanitrostilbene) which is able to burn 64% of its carbon to CO. In addition, the impact sensitivity of 3,3xe2x80x2-diamino-4,4xe2x80x2-azofurazan was determined to be greater than 320 cm while the drop height of HNS was published (Dobratz, xe2x80x9cLawrence Livermore National Laboratory Explosives Handbook. Properties of Chemical Explosives and Explosives Simulantsxe2x80x9d, National Technical Information Service, UCRL-52997, 1981) to be 54 cm (2.5 kg, Type 12).
Pure 3,3xe2x80x2-diamino-4,4xe2x80x2-azoxyfurazan (DAAF) is an orange-yellow crystalline powder having a DSC onset of 248xc2x0 C. and an x-ray crystal density of 1.747 g/cm3. DAAF was found to have a drop height of greater than 320 cm (2.5 Kg, Type 12) and elicited no response to spark ( greater than 0.36 J) or friction ( greater than 36 kg, BAM). DAAF had a measured xcex94Hf=+106 kcal/mole. Low density pellets of DAAF could be pressed neat but high density pellets tended to wafer and therefore required formulation with 5 volume percent of latex Kel-F 800 resin (a chlorotrifluoroethylene/vinylidene fluoride copolymer, available from 3M Company). This allowed pressing of pieces up to a density of 1.70 g/cm3 (97% of theoretical maximum density). A Henkin critical temperature was determined to be 241xc2x0 C. for the Kel-F formulated material and 252xc2x0 C. for the neat material.
The explosive performance properties of DAAF were examined. A poly-xcfx81 test, which determines detonation velocity as a function of density, was performed at two diameters, 0.5 in. and 0.25 in. These two diameters revealed that the detonation velocity was relatively independent of diameter. The detonation velocity of DAF was determined to be 8.0 kilometers per second (km/s) at a density of 1.69 g/cm3. This data was further verified by an unconfined rate stick of pellets at a density of 1.69 g/cm3 and 3 mm in diameter. As evidenced by the witness plate a complete detonation was achieved. Unfortunately, this test was too small to be instrumented accurately to determine detonation velocity. A failure diameter of less than 3 millimeters (mm) is unprecedented in a material which is insensitive to impact. The detonation pressure (PCJ) was estimated to be 299 kbar from a 0.5-inch diameter plate dent at a density of 1.69 g/cm3.
Shock sensitivity was characterized by performing six wedge tests, in which the DAAF was plastic-bonded with 5% Kel-F 800 resin and pressed to 1.705 g/cm3. There have been many variations on the wedge test; the present one is the so-called xe2x80x9cmini-wedgexe2x80x9d test (see Seitz, Shock Waves in Condensed Matter, 531 (1983) and Hill et al., Shock Compression of Condensed Matter, 803 (1995)) which is designed to use a minimal amount (about 7 g) of sample explosive. Material conservation is desirable for screening new explosives, due to cost.
From the wedge testing, it was found that DAAF was quite like HMX so far as shock sensitivity was concerned.
The explosive energy was characterized by performing a standard 1-inch cylinder test on DAAF neat-pressed to 1.691 g/cm3. The cylinder energy was determined to be 1.22 kilojoules per gram (kJ/g) for DAAF. The test consists of a 1.00-inch inner diameter, 0.10-inch wall copper tube filled with explosive and detonated at one end. The pressure of the explosive products expands the tube in a funnel shape. With proper care the tube will typically expand to about three times its initial diameter before it begins to fragment. To achieve this much expansion requires very tight mechanical tolerances and high standards of purity, temper, and grain size for the copper. These requirements are laid out in more detail by Hill et al., Los Alamos Report LA-13442-MS (1998), such report incorporated herein by reference.
The detonation velocity was also measured via ten pin switches, each consisting of 2-mil diameter enameled copper wire. When the detonation passed a wire, the insulation was promptly destroyed and the wire shorted to the tube. This fired an R-C circuit that was observed on an oscilloscope. The resulting detonation velocity was 8.020 mm/xcexcs. The random error, i.e., the standard error in velocity associated with the linear fit to the x-t data, was 2.7 m/s.
Although the azo-compound DAAzF has less available oxygen than DAAF, it has a higher measured xcex94Hf (+128 kcal/mol). Also, the detonation velocity of DAAzF was determined to be 7.6 km/s at a density of 1.65 g/cm3 in the poly-xcfx81 test. The thermal stability of DAAzF was also attractive having a DSC onset of 315xc2x0 C., which is comparable to that of HNS. The previous procedure for preparing DAAzF only yielded inseparable mixtures as did the reduction of DAAF with triphenylphosphine; therefore a new method of synthesizing DAAzF from readily available DAAF was developed. The process involved formation of a hydrazine intermediate from DAAF by reduction with acetic acid and zinc followed by the oxidation to DAAzF by bubbling air through a methanol solution.
The DAAzF, a dark-orange crystalline solid, was found insensitive to impact (H50 greater than 320 cm, Type 12), spark ( greater than 0.36 J) and friction ( greater than 36 kg, BAM). The explosive performance of DAAzF was lower in both velocity and pressure as the increase in heat of formation was not sufficient to offset the drop in oxygen balance compared to the DAAF. The DAAzF was formulated with 5 volume percent latex Kel-F 800 and the detonation velocity as a function of density was determined at two different diameters, 0.5 inches and 0.25 inches. The velocity was more dependent on diameter than with DAAF. Despite this dependence a 3 mm diameter shot at a density of 1.65 g/cm3 detonated cleanly with no confinement. A 0.5-inch diameter plate dent allowed the calculation of a detonation pressure to be 262 kbar at a density of 1.65 g/cm3.
The present invention is more particularly described in the following examples which are intended as illustrative only, since numerous modifications and variations will be apparent to those skilled in the art.
All starting materials were obtained from commercial sources or prepared from the referenced literature. All NMR spectra were obtained on a JEOL GSX-270 spectrometer, and chemical shifts are reported relative to internal tetramethylsilane. Melting points were determined at 2xc2x0 C./min with a Mettler FP1 apparatus and are corrected or by Differential Scanning Calorimetry (DSC) at 2xc2x0 C./min. IR spectra were obtained on a Bio-Rad FTS-40 FTIR spectrometer.